Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Conventional electrochemical double layer capacitors (EDLCs) may include discrete laminated layers such as electrically conductive charge collection electrodes, an ionic conductive electrolyte, and a separator membrane that is ionically conductive, but electrically insulating.
Example components of ELDCs have included high surface area, conductive, porous carbon electrodes; ionic salts in solution as an electrolyte; and a separator membrane of an ionically conductive polymer such as NAFION®. Other examples of ELDCs have employed conductive polymers in the electrodes, either alone or as a composite with conductive carbon or other conductive material. Further examples of ELDCs have employed blends of conductive polymers and polymeric electrolytes to make intermediate layers of a redox based capacitor. Of the electrically conductive polymers, polypyrrole (PPy) has been extensively explored. Various efforts have produced blends of PPy with ionic conductive polymeric electrolytes such as polystyrene sulfonate, polyvinyl alcohol, or polyethylene-glycol. Capacitors generated from such blends may effectively store charge by redox processes in addition to the formation of electrostatic double layers.
Although there have been advances, the present disclosure appreciates that EDLCs that employ conductive polymers may experience undesirable redox effects due to the doping of the mobile ions present in the electrolyte. For example, the described Faradaic processes may lead to asymmetric or irregular charging hysteresis curves, which may reduce the effective capacitor lifetime due to the degradation of reversibility. Such redox degradation may be reduced if the ions of the capacitor electrolyte can be isolated, at least in part, from the conductive polymer chains. Furthermore, separation of ions and counter-ions from the conductive electrodes may be desirable where conductive polymers are employed in non-Faradaic EDLCs.
The present disclosure appreciates that implementing conductive polymers in electrochemical double layer capacitor technology may be a complex undertaking.